Refrigeration system defrost control



Oct. 11, 1966 T. B. WINTERS 3,277,662

REFRIGERATION SYSTEM DEFROST CONTROL Filed Feb. 23, 1965 CABINET TEMPERATURE THERMOSTAT HOT-CLOSED COLD-OPEN DEFROST SWITCH TIME CONTROLLED TIMER [20 "n MOTOR DEFROST THERMOSTAT I HOT-OPEN 3a 30 48 cow-01.0550 40 I 3 EVAPORATOR DEFROST 42 HEATER DRAIN HEATER COMPRESSOR CONDENSER WITNESSES Thomas B. Winters ATTORNEY INVENTOR United States Patent 3,277,662 REFRIGERATION SYSTEM DEFROST CONTROL Thomas B. Winters, Allen Township, Marysville, Ohio,

assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 23, 1965, Ser. No. 434,436 4 Claims. (Cl. 62-155) This invention relates to a refrigeration system of the character in which a defrost cycle is periodically initiated by a timer arrangement.

One object of the invention is the provision of a refrigeration system of the above character having a simplified circuit arrangement.

Another object of the invention is the provision of a refrigeration circuit arrangement in which certain economies are effected.

Broadly, the invention is directed to an arrangement in which the timing motor is connected to be energized under a normal refrigeration condition through a defrost heater circuit, and is connected to be energized under a defrost condition through the windings of the compressor motor. Accordingly, a simplified circuit arrangement is obtained which yields the economies noted.

The single figure of the drawing is a schematic view illustrating one embodiment incorporating the invention by way of example.

The refrigeration components illustrated in the drawing are encased within the suitable cabinet (such as a refrigerator or freezer for example) and include a compressor which pumps refrigerant through a refrigeration system including a condenser 12, a line 14 connecting the condenser to the evaporator 16, and a return or suction line 18 for returning refrigerant to the compressor from the evaporator. Electrical power for energizing the compressor 10, the timer motor 20, and other electrical elements not appearing in the drawing, is delivered by the lines L1 and L2.

Before proceeding to a detailed description of the elements shown in the drawing and their relation to each other, it is noted that the timer motor 20 is connected to be energized through a first circuit including the defrost heater 22 and defrost thermostat 24 when the timer switch 26 is in its broken-line position, and is connected to be energized through an alternate and generally parallel second circuit including the compressor motor windings generally designated 28 when the timer switch 26 is in its illustrated position. In either case, connection to the side L2 of the electrical power supply for completing the circuit is made through the switch 26.

The defrost heater 22 is disposed in heat exchange relation to the evaporator 16 so that the defrosting may be done quickly and effectively. The defrost thermostat switch 24 is also located so as to be responsive to the temperature condition of the evaporator. The defrost thermostat switch detects the defrosted condition by virtue of an elevated temperature and moves from its closed to an open position. It of course again closes when the evaporator temperature is again depressed by operation of the refrigeration system.

The circuit which includes the defrost heater and leads from L1 to the timer motor terminal 30 includes; line 32 connected to one side of the defrost heater, line 34 connecting the other. side of the defrost heater to the defrost thermostat switch 24, line 36 connecting the other side of the defrost thermostat to contact 38 of the timer switch 26, and line 40 connecting contact 38 to terminal 30 of the timer motor.

The alternate circuit for. energizing the timer motor, and which is generally parallel to the just described circuit includes: the motor windings 28 connected to one price side L1 of the power supply, line 42 connecting the motor windings to timer switch contact 44, and line 46 leading to the other terminal 48 of the timer motor.

The third circuit, through which either of the just described alternate circuits may be completed to the other side L2 of the power supply, includes: the movable element 50 of timer switch 26, line 52, a cabinet temperature responsive thermostat switch 54, and the other side L2 of the power supply. The cabinet temperature thermostat 54 is the main control thermostat which, under normal conditions, initiates and terminates the operation of the compressor in accordance with a cabinet temperature above and below, respectively, the set point.

The circuitry 28 for the compressor motor includes an overload protector 56, main motor winding 58, and relay winding 60 in series between the opposite terminals of the motor. The start winding 62, capacitor 64, and relay switch 66 are in parallel with the main winding and the relay winding.

Operation The timer motor 20 and timer switch 26 are adjusted so that during the major portion of the energization time of the motor the switch is maintained in its illustrated position, which is here termed the refrigeration position. For the minor and remaining portion of its energized time during a single cycle, the switch is in its broken-line position, which is here termed the defrost position. Thus, in the normal refrigerating operation of the system, cooling is initiated by the cabinet temperature thermostat 54 moving to a closed position in response to sensing a temperature above the set point temperature. When switch 54 closes the compressor is energized through the circuit traced as.fol1ows: power side L1, compressor motor windings 28, line 42, switch 26 in its refrigeration position, line 52, and switch 54 connected to the other side L2 of the power supply. During the period when the timer switch 26 in its refrigeration position, the timer motor 20 isenergized, depending upon the position of cabinet temperature thermostat 54, through a circuit traced as follows: power side L1, line 32, defrost heater 22, line 34, defrost thermostat switch 24 (assuming it is closed indicating the evaporator is not in either a defrosting or defrosted condition), line 36, switch contact 38, line 40, the timer motor windings (not shown), terminal 48, line 46 to the timer switch contact 44, timer switch 26, line 52, and switch 54 to the other side, L2. It will be appreciated that the timer motor 20, during normal refrigeration operation, accumulates time or is energized only when the cabinet temperature thermostat 54 is closed. Thus, the need for defrost is in a sense correlated with the frequency of the temperature elevation in the cabinet; a condition which in many instances is proportional to the frequency of opening the door to the cabinet.

When the timer motor 20 has accumulated enough energized time to move the switch 26 to its broken-line, i.e., defrost, position, where it connects line 52 to switch terminal 38, the following conditions exist. The defrost heater 22 is energized by being connected directly across the line through the closed defrost thermostat switch 24, timer switch 26 in its defrost position, and the cabinet temperature, thermostat switch 54 which, if open at the time when the defrost cycle is to be initiated by the timer motor, soon moves to a closed position in response to sensing a temperature above the set point temperature. While the defrost heater 22 is energized, the timer motor 20 is energized through the alternate (i.e., motor winding 28) circuit which is traced as follows; side L1, overload protector 56, main winding 58, relay winding 60, line 42, line 46 to terminal 48 of the timer motor, then through the timer motor windings, line 40 to terminal 38 of the timer switch, blade 50 of the timer switch, line 52, and cabinet temperature thermostat 54 to the other side L2 of the power line. The impedance of the timer motor winding is sufficient, since it is in series with the current sensitive relay winding 60 and main winding 58, to prevent the value of current through these windings fi'om actuating the motor start relay switch 66 to a closed position and thereby energizing the compressor motor. Similarly, the timer motor impedance prevents the defrost heater from drawing more than an insignificant current when the alternate circuit energizes the timer motor. After the defrost heater 22 has elevated the evaporator temperature sufficiently to defrost it, the defrost thermostat switch 24 opens and deenergizes the defrost heater. The timer motor 20 will remain energized through the compressor motor windings until the minor time portion is accumulated and the timer switch is actuated back to its normal refrigeration position. The timer motor is then deenergized until the refrigeration system has been operative long enough to close the defrost thermostat 24 in response to sensing a depressed temperature about the evaporator. Of course, when the defrost timer switch 26 moves to its refrigeration position, the compressor will normally immediately be energized because of the elevated cabinet temperature from the defrosting operation causing thermostat 54 to close. With the timer switch 26 back in its normal refrigeration position, the normal refrigerating conditions again exist.

If there is a failure of the defrost thermostat 24 while the defrosting operation is going on, the timer motor will continue to run through the alternate circuit, and then switch the timer switch back to its normal refrigeration condition position so that refrigeration will again be initiated. If the defrost thermostat fails during normal refrigeration, the timer motor ceases to run and a defrost operation can not he again initiated until the failure is remedied.

'I claim as my invention:

1. A refrigeration system having a refrigeration and defrost control arrangement of the character in which a defrost cycle is periodically initiated by electrically operated timer means, including:

an electrical power supply;

a refrigerant compressor and a motor for driving said compressor;

a refrigerant evaporator;

a defrost heater for said evaporator;

a defrost condition responsive switch;

a timer, and a timer-actuated switch having a refrigeration position and an opposite defrost position;

a first circuit connecting one side of said power supply to one terminal of said timer through a winding of said compressor motor;

a second circuit connecting said one side of said power supply to an opposite terminal of said timer, said second circuit including said defrost condition responsive switch and said defrost heater in series therewith;

a third circuit connecting said timer-actuated switch to the opposite side of said power supply, said third circuit including refrigeration condition responsive switch means; i

said timer-actuated switch in said refrigeration position connecting said first terminal to said third circuit, and

in said defrost position connecting said opposite terminal to said third circuit, so that said timer is connected to be energized alternately through said compressor motor and said defrost heater.

2. In a refrigeration system:

an electrical power source;

a refrigerant compressor, and an electric motor for driving said compressor;

a refrigerant evaporator;

a defrost heater for said evaporator;

a defrost condition responsive switch;

a refrigerated space temperature responsive switch;

a timer and a timer-actuated switch having a refrigeration position and a defrost position;

a pair of parallel circuits connecting one side of said power source to opposite contacts of said timeractuated switch, one of said circuits including the windings of said electric motor and being connected to said refrigeration-position contact, and the other of said circuits including said defrost heater and said defrost condition switch in series and being connected to said defrost position contact;

line means connecting each of said timer switch contacts to said timer; and

a third circuit connecting the operable element of said timer switch to the other side of said power source, said third circuit including said refrigerated space temperature responsive switch, so that said timer motor is connected for energization through either of said parallel circuits when said refrigerated space temperature responsive switch is closed.

3. A circuit arrangement for a refrigeration system of the character including an electric motor driven compressor supplying a refrigerant evaporator adapted to be periodically defrosted with a heater, comprising: an electrical power source; a timer motor having opposite terminals connected to opposite contacts of a single-pole, double-throw switch actuated by said timer motor, one of said contacts corresponding to a refrigeration position, and the other corresponding to a defrost position of said switch; alternate circuits connecting one side of said power source to said contacts, one circuit including the windings of said compressor motor connected to said refrigeration position contact, and the other circuit including said heater and a defrost condition responsive switch in series connected to said defrost position contact; and a completing circuit connecting the operable element of said double-throw switch to the other side of said power source; said completing circuit including a thermostatic switch responsive to the temperature of the space being refrigerated so that said timer motor is energized only during closure of said space temperature responsive thermostatic switch. 1

4. A circuit arrangement for a refrigeration system of the character in which a timeractuated switch is moved from one contact to an opposite contact to deenergize a refrigerant compressor motor and energize a defrost heater for an evaporator, comprising:

an electrical power source;

circuit means connecting one side of said power source to said contacts through alternate circuits including, respectively, the windings of said compressor motor connected to said one contact, and said defrost heater and a defrost responsive thermostat switch in series connected to said opposite contact;

'line means connecting said opposite contacts to respectively opposite terminals of said timer; and

a completing circuit connecting the operable element of said timer-actuated switch to the opposite side of said power source, said completing circuit including a thermostatic switch responsive to refrigerated space temperature so that said timer is energized only during closure of said space temperature responsive thermostatic switch.

References Cited by the Examiner UNITED STATES PATENTS 3,063,250 11/1962 Moorman 62-155 3,105,362 10/1963 Gould 62155 X 3,174,297 3/1965 Kuhn et a1 62-455 X ROBERT A. OLEARY, Primary Examiner.

LLOYD L. KING, Examiner. 

3. A CIRCUIT ARRANGEMENT FOR A REFRIGERATION SYSTEM OF THE CHARACTER INCLUDING AN ELECTRIC MOTOR DRIVEN COMPRESSOR SUPPLYING A REFRIGERANT EVAPORATOR ADAPTED TO BE PERIODICALLY DEFROSTED WITH A HEATER, COMPRISING: AN ELECTRICAL POWER SOURCE; A TIMER MOTOR HAVING OPPOSITE TERMNALS CONNECTED TO OPPOSITE CONTACTS OF A SINGLE-POLE, DOUBLE-THROW SWITCH ACTUATED BY SAID TIMER MOTOR, ONE OF SAID CONTACTS CORRESPONDING TO A REFRIGERATION POSITION, AND THE OTHER CORRESPONDIONG TO A DEFROST POSITION OF SAID SWITCH; ALTERNATE CIRCUITS CONNECTING ONE SIDE OF SAID POWER SOURCE TO SAID CONTACTS, ONE CIRCUIT INCLUDING THE WINDINGS OF SAID COMPRESSOR MOTOR CONNECTED TO SAID REFRIGERATION POSITION CONTACT, AND THE OTHER CIRCUIT INCLUDING SAID HEATER AND A DEFROST CONDITION RESPONSIVE SWITCH IN SERIES CONNECTED TO SAID DEFROST POSITION CONTACT; AND A COMPLETING CIRCUIT CONNECTING THE OPERABLE ELEMENT OF SAID DOUBLE-THROW SWITCH TO THE OTHER SIDE OF SAID POWER SOURCE; SAID COMPLETING CIRCUIT INCLUDING A THERMOSTATIC SWITCH RESPONSIVE TO THE TEMPERATURE OF THE SPACE BEING REFRIGERATED SO THAT SAID TIMER MOTOR IS ENERGIZED ONLY DURING CLOSURE OF SAID SPACE TEMPERATURE RESPONSIVE THERMOSTATIC SWITCH. 